Why isn't there any bathrooms in Battu?

It's a rabbit hole building, the same one your Sim uses to sleep and take care of hygiene. It's in the Black Spire area. Just click on it to interact and your Sim will disappear for a few seconds, replenish their need, and come back out. It's done a little differently from the rest of the game. There are also eatery places that do the same thing, only when your Sim goes in, you can choose what they eat from a popup menu. Droid purchases and other items can be acquired the same way from other buildings. You kind of have to look around and click on buildings to get used to where things are.